Re: [patch]: fixing of pmtimer overflow that make Cx states time incorrect

Andrew Morton
2009-01-27T06:52:41Z

The fix looks reasonable to me.

Please always cc linux-acpi@vger.kernel.org on acpi patches.

The patch was quite a mess: inlined code plus an attachment, mangled
email headers, funny characters in the email body, 300-column lines,
etc.

I reproduce a cleaned up copy below.

It's a bit odd that several of these functions (for example,
acpi_idle_enter_bm()) return number-of-microseconds in a plain `int'.
It should be an unsigned scalar - `unsigned int', `u32', `u64', etc.

Also, all those functions have kerneldoc comments, but none of them
document the function's return value, which is a rather important part
of the interface!

Oh well.

From: Alex Shi <alex.shi@intel.com>

We found Cx states time abnormal in our some of machines which have 16
LCPUs, the C0 take too many time while system is really idle when kernel
enabled tickless and highres. powertop output is below:

PowerTOP version 1.9 (C) 2007 Intel Corporation

Cn Avg residency P-states (frequencies)
C0 (cpu running) (40.5%) 2.53 Ghz 0.0%
C1 0.0ms ( 0.0%) 2.53 Ghz 0.0%
C2 128.8ms (59.5%) 2.40 Ghz 0.0%
1.60 Ghz 100.0%

Wakeups-from-idle per second : 4.7 interval: 20.0s
no ACPI power usage estimate available

Top causes for wakeups:
41.4% ( 24.9) <interrupt> : extra timer interrupt
20.2% ( 12.2) <kernel core> : usb_hcd_poll_rh_status (rh_timer_func)

After tacking detailed for this issue, Yakui and I find it is due to 24
bit PM timer overflows when some of cpu sleep more than 4 seconds. With
tickless kernel, the CPU want to sleep as much as possible when system
idle. But the Cx sleep time are recorded by pmtimer which length is
determined by BIOS. The current Cx time was gotten in the following
function from driver/acpi/processor_idle.c:

static inline u32 ticks_elapsed(u32 t1, u32 t2)
{
if (t2 >= t1)
return (t2 - t1);
else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
return (((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
else
return ((0xFFFFFFFF - t1) + t2);
}

If pmtimer is 24 bits and it take 5 seconds from t1 to t2, in above
function, just about 1 seconds ticks was recorded. So the Cx time will be
reduced about 4 seconds. and this is why we see above powertop output.

To resolve this problem, Yakui and I use ktime_get() to record the Cx
states time instead of PM timer as the following patch. the patch was
tested with i386/x86_64 modes on several platforms. and the Cx states
time become good. this patch do not fully remove PM timer for Cx idle
time recording. Maybe it can be recovered if the PM timer get improved in
hardware.

Signed-off-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Yakui.zhao <yakui.zhao@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

drivers/acpi/processor_idle.c | 78 +++++++++++++-------------------
1 file changed, 34 insertions(+), 44 deletions(-)

diff -puN drivers/acpi/processor_idle.c~fixing-of-pmtimer-overflow-that-make-cx-states-time-incorrect drivers/acpi/processor_idle.c
--- a/drivers/acpi/processor_idle.c~fixing-of-pmtimer-overflow-that-make-cx-states-time-incorrect
+++ a/drivers/acpi/processor_idle.c
@@ -185,25 +185,6 @@ static struct dmi_system_id __cpuinitdat
{},
};

-static inline u32 ticks_elapsed(u32 t1, u32 t2)
-{
- if (t2 >= t1)
- return (t2 - t1);
- else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
- return (((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
- else
- return ((0xFFFFFFFF - t1) + t2);
-}
-
-static inline u32 ticks_elapsed_in_us(u32 t1, u32 t2)
-{
- if (t2 >= t1)
- return PM_TIMER_TICKS_TO_US(t2 - t1);
- else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
- return PM_TIMER_TICKS_TO_US(((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
- else
- return PM_TIMER_TICKS_TO_US((0xFFFFFFFF - t1) + t2);
-}

/*
* Callers should disable interrupts before the call and enable
@@ -397,7 +378,8 @@ static void acpi_processor_idle(void)
struct acpi_processor_cx *cx = NULL;
struct acpi_processor_cx *next_state = NULL;
int sleep_ticks = 0;
- u32 t1, t2 = 0;
+ ktime_t kt1, kt2;
+ u32 idle_time;

/*
* Interrupts must be disabled during bus mastering calculations and
@@ -543,15 +525,16 @@ static void acpi_processor_idle(void)
break;

case ACPI_STATE_C2:
- /* Get start time (ticks) */
- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ /* Get start time */
+ kt1 = ktime_get();
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
/* Invoke C2 */
acpi_state_timer_broadcast(pr, cx, 1);
acpi_cstate_enter(cx);
- /* Get end time (ticks) */
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ /* Get end time */
+ kt2 = ktime_get();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
/* TSC halts in C2, so notify users */
@@ -559,7 +542,7 @@ static void acpi_processor_idle(void)
mark_tsc_unstable("possible TSC halt in C2");
#endif
/* Compute time (ticks) that we were actually asleep */
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);

/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
@@ -604,14 +587,15 @@ static void acpi_processor_idle(void)
ACPI_FLUSH_CPU_CACHE();
}

- /* Get start time (ticks) */
- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ /* Get start time */
+ kt1 = ktime_get();
/* Invoke C3 */
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
acpi_cstate_enter(cx);
- /* Get end time (ticks) */
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ /* Get end time */
+ kt2 = ktime_get();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));
if (pr->flags.bm_check && pr->flags.bm_control) {
/* Enable bus master arbitration */
atomic_dec(&c3_cpu_count);
@@ -624,7 +608,7 @@ static void acpi_processor_idle(void)
mark_tsc_unstable("TSC halts in C3");
#endif
/* Compute time (ticks) that we were actually asleep */
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);
/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

@@ -1455,7 +1439,8 @@ static inline void acpi_idle_do_entry(st
static int acpi_idle_enter_c1(struct cpuidle_device *dev,
struct cpuidle_state *state)
{
- u32 t1, t2;
+ ktime_t kt1, kt2;
+ u32 idle_time;
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);

@@ -1476,14 +1461,15 @@ static int acpi_idle_enter_c1(struct cpu
if (pr->flags.bm_check)
acpi_idle_update_bm_rld(pr, cx);

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

local_irq_enable();
cx->usage++;

- return ticks_elapsed_in_us(t1, t2);
+ return idle_time;
}

/**
@@ -1496,7 +1482,8 @@ static int acpi_idle_enter_simple(struct
{
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
- u32 t1, t2;
+ ktime_t kt1, kt2;
+ u32 idle_time;
int sleep_ticks = 0;

pr = __get_cpu_var(processors);
@@ -1533,18 +1520,19 @@ static int acpi_idle_enter_simple(struct
if (cx->type == ACPI_STATE_C3)
ACPI_FLUSH_CPU_CACHE();

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get();
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
/* TSC could halt in idle, so notify users */
if (tsc_halts_in_c(cx->type))
mark_tsc_unstable("TSC halts in idle");;
#endif
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS( idle_time);

/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
@@ -1556,7 +1544,7 @@ static int acpi_idle_enter_simple(struct

acpi_state_timer_broadcast(pr, cx, 0);
cx->time += sleep_ticks;
- return ticks_elapsed_in_us(t1, t2);
+ return idle_time;
}

static int c3_cpu_count;
@@ -1574,7 +1562,8 @@ static int acpi_idle_enter_bm(struct cpu
{
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
- u32 t1, t2;
+ ktime_t kt1, kt2;
+ u32 idle_time;
int sleep_ticks = 0;

pr = __get_cpu_var(processors);
@@ -1644,9 +1633,10 @@ static int acpi_idle_enter_bm(struct cpu
ACPI_FLUSH_CPU_CACHE();
}

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

/* Re-enable bus master arbitration */
if (pr->flags.bm_check && pr->flags.bm_control) {
@@ -1661,7 +1651,7 @@ static int acpi_idle_enter_bm(struct cpu
if (tsc_halts_in_c(ACPI_STATE_C3))
mark_tsc_unstable("TSC halts in idle");
#endif
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);
/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

@@ -1672,7 +1662,7 @@ static int acpi_idle_enter_bm(struct cpu

acpi_state_timer_broadcast(pr, cx, 0);
cx->time += sleep_ticks;
- return ticks_elapsed_in_us(t1, t2);
+ return idle_time;
}

struct cpuidle_driver acpi_idle_driver = {
_